X-ray diffractometer diaphragm which is synchronously rotated with the specimen



NOV. 12, 1968 w, SCHUEPHAKE ET AL 3,411,000

X-RAY DIFFRACTOMBTER DIAPHRAGM WHICH IS SYNCHRONOUSLY ROTATED WITH THESPECIMEN Filed April 14, 1965' INVENTORS Po/f Werner ficflfie p/yaie ilf/he/m G/j/mberg doac/w'rn Pic er United States Patent ABSTRACT OF THEDISCLOSURE A diaphragm arrangement, essentially comprising an aperturediaphrgam with two diaphragm plates, for use in an X-ray diffractometer,wherein the surface of a rotatable specimen is intended to be fullyscanned, whereby the movement of the diaphragm plane is synchronous withthe movement of the specimen, so that the diaphragm plane is invariablyat right angles to the surface of the speciman.

The invention relates to an automatic aperture diaphragm for X-rayexposures of diffraction diagrams, using a diffractometer (counting tubegoniometer).

When making exposures of X-ray diagrams with a diffractometer, theintensity of the interferences decreases considerably with increasingdiffraction angle 20. The hitherto usual aperture diaphragms having twodiaphragm plates remain stationary during the exposure, whereby thecross-section of the pencil of X-rays incident on the preparationremains unchanged. In this case, therefore, always the same X-rayintensity is used. On account of the e-movement of the preparation, thesurface irradiated by the X-ray becomes smaller by 1/ sin 0 as theincidence angle 0 increases. As a result, an always smaller number ofcrystallites diffracts intensity into the interferences and increasesthe random fluctuations of the intensity on account of a small number ofeffective crystallites, i.e., the influence of crystal statistics.Consequently, in order to produce a satisfactory diffraction diagram, itwas formerly frequently necessary to expose several component regions ofthe diffraction diaphragm with a different setting of the diaphragmaperture.

The invention has for its object to provide an aperture diaphragm withwhich it is possible in simple manner, at all angles of diffraction,always to illuminate the same surface of the preparation with the pencilof X-rays. It has surprisingly been found that this object can beachieved by the aperture diaphragm being so arranged to be rotatableabout the centre line 7 between the diaphragm plates 1, 2 that the plane6 of the diaphragm is always parallel to the surface of the rotatablepreparation at all angles of diffraction.

With the arrangement according to the invention, a departure is madefrom the hitherto usual principle and it is the surface of thepreparation affected by the X-ray radiation which is kept constantinstead of the cross-section of the pencil of X-rays and thus instead ofthe primary ray intensity. As a result, with increasing angle ofincidence 0, the intensity of the primary ray is increased and thedecrease in intensity of the interferences with higher angles ofdiffraction is partially compensated for. In addition, on account of theconstancy of the affected surface or area ofthe preparation, the numberof effective crystallites remains the same and thus the fluctuations inintensity because of the crystal statistics with interferences of higherangle of diffraction 20 are not increased.

Using such rotatable diaphragm, it is possible without any effort tomeasure up to the largest angles of diffraction without the diaphragmaperture itself being changed. The rotation of the diaphragm thus hasthe same effect as when the diaphragm is opened or closed. If therotation of the diaphragm takes place according to the invention incomplete synchronism with the a-movement of the preparation and in factto such an extent that the plane of the diaphragm always remainsparallel to the surface of the preparation, that path of rays is alwaysso limited by one inner edge of each plate that the same surface of thepreparation is illuminated. The intensity of the X-rays incident on thepreparation accordingly varies proportionally with the sin 19 with theaperture diaphragm according to the invention. Since that part of thecombined polarisation, Lorentz and geometrical factor for powderexposures which is dependent on angle has the form l-l-eos 0 sin 0 cos 0this factor is simplified when using the diaphragm arrangernentaccording to the invention, taking into account the diaphragm factorB=sin 0 to 1+cos 0 sin 0 The form of the diaphragm elements proper is ofno decisive importance for the invention. In its simplest form, thediaphragm consists of two plates, which are arranged on a rotatablesupport. It is possible for the distance between the inner diaphragmedges to be adjustable in order to adapt the masked X-ray beam to thesize of the preparation. With the rotation of the diaphragm about thecentre line between the diaphragm plates, one inner edge of each platethen determines the width of the diaphragm aperture. The form of theseeffective diaphragm edges in their turn are dependent on the shape ofthe preparation to be measured. For example, if this preparation isrectangular or square, the diaphragm edges are naturally rectilinear andare situated at right angles to the plane of the diffractometer circle.However, if the preparation to be measured is round, the inner diaphragmedges are advantageously made circular in order to illuminate a large aspossible surface of the preparation. As plane of the diaphragm withinthe terms of the invention, there is to be indicated that plane whichextends between the two diaphragm plates and which also passes throughthe two effective diaphragm edges and through the centre line.

It is an additional advantage of the diaphragm arrangement according tothe invention that those surfaces of the two diaphragm plates which aresituated in the plane of the diaphragm act as an antidiffusion screen.This applies more particularly in respect of that surface which passesthrough the plane of the diaphragm and which faces the secondary beam.The effective inner diaphragm edges do in fact not only limit theprimary beam, but they are also the starting point of a disturbingscattered radiation. This scattered radiation is stronger as the anglesof the exposed diffraction diagram are smaller. By a suitable dimensionof the plate surfaces, it is thus possible according to the invention toachieve the effect that the receiver gap is screen off from thescattered radiation. This antidiffusion screen is effective down to verysmall angles of diffraction, so that measurements down to a diffractionangle of about 20x10 can be made.

The synchronous rotation of the diaphragm with the e-movement of thepreparation can be achieved in various ways. The movement willpreferably be effected mechanically and the simplest form here is todrive the diaphragm through a toothed wheel gear.

The invention is to be more fully explained by reference to theaccompanying drawing.

FIGURE 1 is a front elevational view of the diaphragm;

FIGURE 2 is a side elevational view of the diaphragm;

PLG=

PLBG= FIGURE 3 is a sectional view taken on line 33 of FIGURE 1.

FIGURE 4 shows the arrangement of the diaphragm device on thediffractometer and the path of rays with an angle of diffraction 20.

The aperture diaphragm according to the invention consists essentiallyof two metal plates 1 and 2 which are disposed in juxtaposition andoffset relatively to one another, each plate being provided with such anopening that together they form the window 3. This window is thediaphragm aperture proper, which can optionally be adapted to the sizeof the preparation by displacement of the halves of the plates. The twodiaphragm plates are arranged on the rotatable support 4, which carriesthe gear wheel 5 at the bottom end. The plane 6 extending between theplates is designated according to the invention as the diaphragm plane,while the centre line 7 extends through the centre of the support 4 andthus of the gear wheel 5. As the X-ray beam passes through the aperturediaphragm, the width of said beam is limited by the two diaphragm edges8 and 9 the manner in which the aperture diaphragm operates will beparticularly clear by considering FIGURE 4. The aperture diaphragm issituated between the focal spot 11 of the X-ray tube and the preparation12 in the path of rays of the diffractometer, which is represented bythe diifractometer circle 10, the said diaphragm being represented inFIGURE 4 by the two effective edges 8 and 9 of the two diaphragm plates1 and 2. The spacing of the two edges 8 and 9 from the centre line is soadjusted in this case that the preparation 12 is just fully illuminated.The preparation 12 is obviously arranged on a support similar to thesupport 4 of the diaphragm, so that it is in the plane of the rays.Furthermore, the preparation support also has arranged thereon a gearwheel 13, which is of the same size (diameter and number of teeth) asthe gear wheel 5. The two gear wheels 5 and 13 intermesh by means of anauxiliary gear wheel 14, which is resiliently mounted by means of thespring 15, as shown in FIGURE 4.

In this way, while making the exposure of an X-ray diffraction diagramduring the fl-movement of the preparation, the diaphragm plane 6 isadvanced by an angle which is the same as that of the preparation 12 bythe action of the gear wheels 13, 14 and 5. The plane 6 of the diaphragmthus always remains parallel to the surface of the preparation. Anadditional effect resulting from the parallel relationship between theaperture diaphragm and the surface of the preparation is that thesurfaces 16 and 17 of the two diaphragm plates lying in the diaphragmplane 6 prevents the scattered radiation emanating from the diaphragmedges 8 and 9 passing into the radiation receiver 18. The scattered rayshave in fact positively not passed beyond the plane 6 of the diaphragm.

It is obvious that the shafts of the gear wheels 5, 13 and 14 must beperpendicular to the diffractometer circle and in addition the shaft ofthe gear wheel 5 must be adjustable perpendicularly of the primary beamin the plane of the diffractometer circle.

We claim:

1. A diaphragm arrangement for use with an X-ray diffractometercomprising:

a pair of diaphragm plates mounted on a first turntable,

the turntable mounted for rotary motion on an axis between thediaphragms,

a preparation plate supported for rotatable motion on a secondturntable,

and means for keeping the pair of diaphragm plates and the preparationplate parallel.

2. The apparatus according to claim 1 wherein the means for keeping theplates parallel comprise, first gear teeth formed about the edge of thefirst turntable, second gear teeth formed about the edge of the secondturntable, and an idler gear in mesh with the first and second gearteeth.

References Cited UNITED STATES PATENTS 1/1959 Nefl" 2505l.5 7/1961Delong et al 250-495

